This invention relates to translucent and transparent dentifrice compositions with optimum abrasiveness and favorable feeling.
In general, translucent or transparent dentifrices are prepared by admixing a humectant, a binder and other ingredients with water to provide a transparent vehicle having a refractive index of 1.40-1.47 and blending the vehicle and an amorphous silica-family abrasive having substantially the same refractive index as that of the vehicle. As the silica-family abrasive for translucent or transparent dentifrices, anhydrous or hydrated amorphous silicas are usually used. Anhydrous or hydrated amorphous silicates such as sodium or potassium aluminosilicates in which SiO.sub.2 is inter-bonded with 1-10% by weight of alumina, magnesia or other metal oxides are also used. U.S. Pat. Nos. 3,836,641, 3,864,470, 3,906,090, 3,911,102, 3,911,104, 3,946,108, 4,036,949 and 4,066,745, and British Pat. Nos. 1,348,492, 1,349,373, 1,347,650, 1,400,153 and 1,433,743 disclose various silica-family abrasives.
Through a series of experiments, the inventors have found that amorphous silicas in which SiO.sub.2 is partially inter-bonded with less than 1% by weight of metal oxide give highly transparent dentifrices, but have poor abrasiveness and stain removal. Crystalline silicas can satisfy abrasiveness, but will harm the tooth surface because they are not available in fine particles. On the other hand, amorphous silicates bring about less transparent dentifrices as compared with amorphous silicas. Moreover, a humectant having a high refractive index such as glycerine or sorbitol must be blended in a larger amount because the amorphous silicates have relatively high refractive indexes. The dentifrices containing such a larger amount of the humectant have unfavorable taste and feeling.
Accordingly, the prior arts of translucent and transparent dentifrices are more or less impractical since problems remain with respect to abrasiveness, feeling and stand-up quality.